Light emitting diodes (LEDs) are inherently not spatially uniform. The non-uniformity may come from non-radiative metal contacts, uneven phosphor distribution, or the use of multiple LEDs emitting the same or different colors in one optical system. For broad beam angles, spatial variation at illuminated plane may be tolerated. As the beam angle is decreased, spatial non-uniformities become much more distinguishable.
In the conventional art, secondary optics may include one or multiple LEDs of the same or different colors. If the secondary optics projects the source intensity onto a surface, spatial separations of the source create spatial separation at the illuminated plane. LEDs of different colors illuminate a given plane including chromatic spatial separation. One LED with spatial non-uniformities may project spatial non-uniformities to the illuminated plane.
Homogenizers have been used in projection systems. However, the homogenizers were often remote from the light source and included lenses upstream of the homogenizer to focus light into the homogenizer. In a DLP system, the ultra-high performance (UHP) source is imaged into the entrance of the light bar.
There remains a need however to achieve uniform spatial homogenization from one or multiple LEDs for narrow beam angles.